Questions & Answers about Zij merkt dat het heel donker wordt.
Why is the verb wordt at the very end of the sentence?
This is the main rule for subordinate clauses! The word dat (that) links the two parts of the sentence together. Whenever you use a subordinating conjunction like dat, omdat (because), or als (if), the verb in that part of the sentence gets pushed all the way to the end. So instead of het wordt heel donker, it becomes dat het heel donker wordt.
The English translation says "is getting", but doesn't worden mean "to become"?
Yes, worden literally means "to become". In Dutch, you use worden to talk about a change of state. While in English you usually say "it is getting dark," in Dutch you say it is "becoming" dark (het wordt donker). Remember that Dutch does not use an "is + -ing" form, so the simple present tense is used here.
Could I use ze instead of zij in this sentence?
Yes, you absolutely can. Ze is the normal, unstressed word for "she". You use zij (as shown in this sentence) when you want to put a little extra emphasis on her specifically. For example, you might use zij to show that she notices it's getting dark, even if her friends haven't noticed it yet.
Why do we use het (it) before heel donker?